1. Field of the Invention
This invention relates to a lens barrel of a lens system for a camera, and more particularly to a lens barrel of a lens system for a photographic camera in which at least the operating ring thereof is made of synthetic resin.
2. Description of the Prior Art
In the photographic camera, it is desirable to reduce the weight of the camera body including the lens. The lens barrel of the lens system attached to the camera is usually made of metal such as aluminium in its operating ring and lens holding ring and other parts thereof. The lens barrel including parts made of metal is heavy and is desired to be lightened by replacing the metal parts by plastics or other synthetic resin parts. By replacing the metal parts by the synthetic resin parts, not only the weight thereof is reduced but also the cost thereof is lowered.
On the other hand however, the synthetic resin parts are disadvantageous in that the manufacturing accuracy and the operational accuracy thereof are not so high as the metal parts. From this viewpoint, it has generally been practiced to use the synthetic resin parts as the distance ring, the aperture control ring, the focal length varying ring and other manually operated rings in the camera. The operating rings like these control rings made of synthetic resin do not affect the optical performance of the lens barrel. However, these rings are disadvantageous in that the operation thereof sometimes cannot be smoothly made. This is because the operating rings made of synthetic resin are easily deformed by forces applied thereto in the radial direction. Particularly when these rings are manually operated, the rings are compressed by fingers and imparted with radially inwardly acting forces. On such occasions, the internal structure of the lens barrel including members driven by the operating rings are imparted with unnecessary forces and the operation of the internal structure is not properly made or the smooth operation thereof is prevented.
For instance, the deformation or strain of the distance ring made in the axial direction and the radial direction imparts an abnormal external force to a helicoid mechanism used for converting a rotating movement of the operating ring to an axial movement of the lens mounted therein. Consequently, a very large operating force is required to rotate the distance ring and the smooth operation thereof is prevented.